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Alevel Physics (Edexcel) > Topic 9 > Flashcards

Topic 9 Flashcards

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1
Q

How do you convert from Celsius to Kelvin

A

Add 273

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2
Q

Why is the absolute scale used

A

It doesn’t arbitrarily depend on the properties of a given substance.
0K (absolute zero) means that the particles have minimum internal energy

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3
Q

Describe the arrangement and energy of particles in a solid, a liquid and a gas

A

Solid- regular arrangement, vibrate around fixed positions
Liquid - close together, constantly moving past each other
Gas - spaced very far apart, free to move in all directions

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4
Q

How does Brownian motion give evidence for the particle model of matter

A

Smoke particles suspended in air can be seen to move randomly in all directions. This must be as a result of random collisions with particles making up the air

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5
Q

What is internal energy

A

The sum of the potential and kinetic energies of a system

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6
Q

True or false: At a given temperature, all particles in a material have the same kinetic energy

A

False. The kinetic energies will be randomly distributed around a central ‘most likely’ amount

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7
Q

How can you increase the thermal energy of a system

A

We can increase it by heating it up or doing work on the object

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8
Q

Explain the energy changes that occur during a change of state

A

During change of state the potential energy of the particles change but the kinetic energies don’t change

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9
Q

What equation can be used to determine the energy required to change the temperature of a substance

A

E = mcΔθ

Where E = energy, m = mass, c = specific heat capacity, Δθ = temperature change

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10
Q

What is the specific heat capacity of substance

A

The energy required to raise the temperature of 1kg of a substance by 1K

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11
Q

Give the equation to workout the energy for a change of state

A

E = ΔmL
Where E = energy, Δm = mass change, L = specific latent heat (‘of fusion’ if melting/freezing, ‘of vaporisation’ if condensing/evaporating)

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12
Q

What is the specific latent heat of a substance

A

The energy required to change the state per unit mass of a substance, while keeping the temperature constant

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13
Q

In an experiment to find ‘c’ for water, lots of energy input escapes to the surrondings. Will this lead to an over or underestimate of specific heat capacity

A
  • An overestimate
  • Specific heat capacity is calculated as: c = E / (mΔθ)
  • The energy input will be used, but the temperature change of the water will be lower than it should be due to the escaped energy - therefore c will be too high
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14
Q

What is Avogadro’s constant (in words)

A

The number of atoms there are in one mole of a substance

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15
Q

How is the motion of gas molecules described

A

Gas molecules move with Brownian motion, which is the random motion of molecules caused by collisions with larger particles

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16
Q

How does a gas exert a force on its container

A
  • The molecules collide with the walls of their container
  • Collisions cause a change in momentum
  • A change in momentum produces a force equal to the rate of change of momentum
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17
Q

What does Boyle’s law state

A

When a gas is at a constant temperature, pressure and volume are inversely proportional to each other

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18
Q

Explain Boyle’s Law

A
  • When the volume of a gas increases, the space between molecules increases and so the time between collisions is larger.
  • This causes the rate of collisions and so the rate of change of momentum decreases.
  • This means the force exerted is lower, causing a decrease in pressure
19
Q

What does Charles’ law state

A

When a gas is at a constant pressure, the volume is directly proportional to the absolute temperature

20
Q

Explain Charles’ Law

A
  • As temperature increases, the average Kinetic energy of the molecules increases
  • Pressure is constant so the force and so also the rate of change of momentum, must remain constant
  • To achieve this, the volume increases so the faster speed of the molecules is compensated by there being larger gaps between them
21
Q

What does the Pressure Law state

A

When a gas has a fixed volume, pressure is directly proportional to the absolute temperature

22
Q

Explain the Pressure Law

A
  • As temperature increases, the average kinetic energy, and so the speed of the molecules also increases
  • This increases the rate of collisions, and so produces a larger rate of change of momentum
  • This leads to a greater force exerted and so an increase in pressure
23
Q

In kinetic theory, what is assumed about the gasses involved

A
  • The gas contains a large number of molecules
  • The molecules are identical to each other
  • All collisions between molecules and the walls of their container are perfectly elastic
  • The time taken for collisions is negligible compared to the time between collisions
  • There are no intermolecular forces between molecules
  • Molecules are in constant random motion
  • The gas particles obey Newton’s Laws of motion
24
Q

What follows all the assumptions made in kinetic theory

A

Ideal gases

25
Q

State the relationship between volume and pressure for a given quantity of gas at a fixed temperature

A

Pressure is inversely proportional to volume

P = k/V

26
Q

State the relationship between volume and temperature for a given quantity of gas at a fixed pressure

A

Volume is directly proportional to temperature

V = kT

27
Q

State the relationship between pressure and temperature for a given quantity of gas with a fixed volume

A

Pressure is directly proportional to temperature

P = kT

28
Q

Combine the relationships between pressure, volume and temperature into a single expression, with a constant

A

(pV)/T = constant

29
Q

State the ideal gas equation

A 
pV = NkT
pV = nRT
30
Q

What does ‘k’ represent in the ideal gas equation

A

THe Boltzmann constant (= 1.38x10^-23 J/K)

31
Q

What does ‘N’ represent in the ideal gas equation

A

The number of molecules

32
Q

How do you convert between the number of moles and number of molecules in a sample

A

Multiply the number of moles by the Avagadro constant

33
Q

State three ideal gas assumptions about the motion of the particles in an ideal gas

A
  1. The particles obey Newton’s Laws of motion
  2. They travel in straight lines
  3. They are in random motion
34
Q

What assumption is made about the forces between molecules in an ideal gas

A

There are no intermolecular forces acting between collisions

35
Q

What can be said about the internal energy of an ideal gas

A

There are no intermolecular forces and so there is no potential energy. This means the internal energy is entirely kinetic energy

36
Q

Describe the collisions between the molecules in an ideal gas

A

The collisions between molecules and between molecules and the container are elastic

37
Q

What assumptions are made about the size of the molecules in an ideal gas

A
  1. The volume of the molecules is negligible in comparison to the volume of the container
  2. All the molecules are identical
38
Q

State the equation linking the pressure and volume of a gas to the speed of its molecules

A

pV = 1/3 Nm

39
Q

What is Wien’s Law

A

Peak wavelength x Temperature = 2.898x10^3
λxT = 2.898x10^3

Peak wavelength is the wavelength at which the emitted radiation is most intense i.e. there is a peak on the black body radiation curve

40
Q

What is the peak wavelength

A

The peak wavelength is the wavelength at which the emitted radiation is most intense i.e. there is a peak on the black body radiation curve

41
Q

What is the Stefan-Boltzmann law equation

A

L = σAT^4
L is power output (W), σ is the Stefan-Boltzman constant, A is the surface area of the black body (m^2) and T is te temperature (K)

42
Q

What equation can be used to calculate the kinetic energy of a molecule from its temperature

A

EK = 3/2 kT

k is the boltzmann constant and T is the temperature (K)

43
Q

What is meant by the root mean square speed

A

The square root of the mean of the squares of the speeds of the molecules

44
Q

What is an ideal gas

A

A gas where:

  • The gas molecules don’t interact with each other
  • The molecules are thought to be perfect spheres

Alevel Physics (Edexcel) (13 decks)

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